Energy Units and Conversions

Energy Units and Conversions

by Dennis Silverman

U. C. Irvine, Physics and Astronomy

 

Energy Units and Conversions

1 Joule (J) is the MKS unit of energy, equal to the force of one Newton acting through one meter.
1 Watt is the power of a Joule of energy per second
Power = Current x Voltage (P = I V)
1 Watt is the power from a current of 1 Ampere flowing through 1 Volt.
1 kilowatt is a thousand Watts.
1 kilowatt-hour is the energy of one kilowatt power flowing for one hour. (E = P t).
1 kilowatt-hour (kWh) = 3.6 x 10⁶  J = 3.6 million Joules
1 calorie of heat is the amount needed to raise 1 gram of water 1 degree Centigrade.
1 calorie (cal) = 4.184 J
(The Calories in food ratings are actually kilocalories.)
A BTU (British Thermal Unit) is the amount of heat necessary to raise one pound of water by 1 degree Farenheit (F).
1 British Thermal Unit (BTU) = 1055 J (The Mechanical Equivalent of Heat Relation)
1 BTU = 252 cal  = 1.055 kJ
1 Quad = 10¹⁵ BTU  (World energy usage is about 300 Quads/year, US is about 100 Quads/year in 1996.)
1 therm = 100,000 BTU
1,000 kWh = 3.41 million BTU

Power Conversion

1 horsepower (hp) = 745.7 watts

Gas Volume to Energy Conversion

One thousand cubic feet of gas (Mcf) -> 1.027 million BTU = 1.083 billion J = 301 kWh
One therm = 100,000 BTU = 105.5 MJ = 29.3 kWh
1 Mcf -> 10.27 therms

Energy Content of Fuels

Coal                         25  million BTU/ton
Crude Oil                 5.6 million BTU/barrel
Oil                         5.78 million BTU/barrel = 1700 kWh / barrel
Gasoline                   5.6 million BTU/barrel (a barrel is 42 gallons) = 1.33 therms / gallon
Natural gas liquids    4.2 million BTU/barrel
Natural gas                      1030 BTU/cubic foot
Wood                       20 million BTU/cord

CO2 Pollution of Fossil Fuels

Pounds of CO2 per billion BTU of energy::
Coal            208,000 pounds
Oil               164,000 pounds
Natural Gas 117,000 pounds

Ratios of CO2 pollution:
Oil / Natural Gas = 1.40
Coal / Natural Gas = 1.78

Pounds of CO2 per 1,000 kWh, at 100% efficiency:
Coal             709 pounds
Oil                559 pounds
Natural Gas  399 pounds